Fuel burner safety control system



Jan. 9, 1951 J. M. WILSON 2,537,291

FUEL BURNER SAFETY CONTROL SYSTEM Filed March s, 1947 4:a sheets-sheet 1 :Snventor GttornegI Jan. 9, 1951 J. M. wlLsoN FUEL BURNER SAFETY CONTROL SYSTEM Filed March 3, 1947 2 Sheets-Sheet 2 Fvg. z.

nventor JOHN M. WILSN Gttorneg Patented Jan. 9, 1951 FUEL BURNER CONTROL SYSTEM John M. Wilson, Minneapolis, Minn., assigner to Minneapolis-Honeywell Regulator Company,

Minneapolis, Minn.,va corporation of Delaware AppneauoaMu-h s, 1947, serial No. 731,998

l This invention relates broadly to automatic control apparatus for fuel burners and is generally directed to that type of system which is put j in operation by a room thermostat or other tem- I perature sensitive element. In such a system it is necessary to provide a combustion responsive device which will sive an indication of flame.. As there is always a possibility of. thecombustion responsive device operating falsely, it is necessary to provide a safety shut-down which will prevent the system from operating when such a condition exists.

y In conventional fuel burner control apparatus, it is customary to provide a timed safety switch which is energized at the time the room thermostat closes and starts the burner in operation and is deenergized upon operation of a combustion responsive device. In my improved apparatus I 1s claim. (c1. 15s-2s) Still another object of my invention is to provide in cooperation with the above described objects in apparatus that will prevent the appa.-4

ratus from causing a fuel burner from going into operation except in the proper timing sequence should a momentary power failure occur.

Other objects of the invention will be readily apparent upon consideration of the specification, claims and drawings of whichz.

Figure 1 is a diagrammatic showing of one particular embodiment'of my invention with the utilize this safety switch 'to prevent the system v from operating when the combustion responsive device indicates combustion and the burner is not in operation. As the safety shut-down may indicate either a name failure or equipment failure, it may, in certain cases, be advisable to distinguish between flame failure and equipment failure by making it impossible to deenergize the control apparatus until the equipment has been repaired.

Added to the safety features of my safety switch circuit and working in conjunction therewith, I provide a further safety feature that prevents the system from going back into operation in the wrong sequence upon a momentary power failure when the flame responsive device does not become deenergized either because of a. sticking relay or some other fault'that will hold the flame responsive device in an energized position.

It is therefore an object of the present invention to provide apparatus which will be shut down upon the failure of the combustion responsive device to correctly indicate a name.

A further object is to utilize the control apparatus safety switch to obtain a shut down of the system upon a name failure or failure of the combustion responsive device to operate correctly.

A still further object is to provide control ap- 4 paratus 'with a safety -shut down which when riication of my invention which has added falle safe features.

In referring to Figure 1 of the drawings, the

.power lines I and 2 are connected through the control system to the housing 3 which contains an ignition device l, burner motor 5, and a flame deliiecting element 6 which is shown as a photoce v In the control system proper, a transformer Il has a primary winding II connected to the input power lines I and 2. A secondary winding of transformer I0 has a tap I4 which divides the winding into two parts designated as l2 and I2, Numeral I5 designates a relay which has a winding I6, adapted when energized to move the relay armature I1. The relay armature I1, when energized by winding I6, will move relayswitch arms I9, 2l and 23 into engagement with their respective contacts I8, 20, and 22. Switch arms I9, 2i and 23 are normally biased out of engage-l ment with these contacts by-any suitable means (not shown).

A safety switch device 25 consists of a pair of biased open switch arms 21 and 28 which are maintained in a closed position by a. bimetal element 29. A heater element 2B is mounted adjacent to the bimetal element so that when it is energized it will cause the element to move in an upward direction. When the bimetal element 2l has been warped sufficiently to allow the contacts of switch arms 21 and 28 to break, the switch arm 21 will move under the bimetal element 29 due to a biasing action placed thereon, .and will hold the element 29 in its lwarped position. A reset member 30 has been provided which when thrust toward the right will move the switch arm 21 from under the element 29 and allow the element-2l to come back into the position shown on the upon a temperature decrease the switch arm 42 engages the contact 43 at a temperature slightly -above that when the switch arm 44 engages the Il. Switch arms 80 and 82 are normally biased i open by any suitable means (not shown).

An evacuated electron discharge device 85 contains an anode 88, a control element in the form of la. grid 81, a cathode 88, and a illament 88. A grid resistor is connected to the control element 81. A condenser 1|, resistor 12, resistor 13, and condenser 14, act as biasing elements in a manner to be described hereinafter. A resistor acts as a current limiting resistor in an electrical circuit !or the photocell 8. This last named circuit comprises an electronic name detector of the type completely described in my copending application, Serial No. 465,476, iiled November 13, 1942, now Patent No. 2,448,503, granted August 31, 1948.

Operation The parts shown in Figure 1 occupy the position they would normally occupy when the room thermostat 40 has been satisfied. Under these conditions the burner motor 5 and the ignition device 4 will be deenergized and there will be no heat supplied to the system. As soon as the temperature in the space in which the thermostat 40 is located has decreased sumciently to cause the blades 42 and 44 to move into engagement with their respective contacts 43 and 45, an. energizing circuit -for the relay |5 will have been established by way of conductor 80, relay winding I8, conductor 8|, terminal 82, switch contact 43, blade 42, blade 44, switch contact 45, terminal 03, conductor 84, switch contact 8| switch arm 80, conductor 85, terminal 88, switch contacts 21 and 28, terminal 81. conductor 83, safety switch heater 28, conductor 88, junction I0, and conducor 0| back to the secondary winding of transformer |0.

With the energizing of relay 5, the switch arm 23 is moved into engagement' with contact 22 and forms an energizing circuit for the ignition device 4 and the motor 5 by a circuit connection from junction 92, conductor 83, switch arm 23, switch contact 22, conductor 04, junction 85, and to the ignition device through switch contact 83, switch arm 82, conductor 88, terminal 01, conductor 58, through the ignition device 4, to conductor 99. and terminal |00 to junction |0| of line 2. The circuit for the burner motor 5 is completed from the Junction 95 of the circuit already traced through the conductor |02, terminal |03, conductor |04, through the burner motor 5, to conductor |05, and terminal |08 to Junction |01 of line 2.

Energization of relay I5, in addition to energizing the ignition device 4 and the burner motor 5, provides a self-holding circuit which may be traced from the secondary winding of transformer I throughV conductor 80, relay winding I8, conductor 8|, terminal 82, switch contact 4l, switch blade 42, terminal 48, terminal |28, conductor I I0, switch arm 2|, switch contact 20, conductor |3|, terminal 88, switch contacts 21 and 20, terminal 81, conductor 88, energizing element 25,

conductor 89, junction 80, and conductor 8| back to the secondary winding. As the closing of switch arm I8 and switch contact I0 oi' the relay I5 forms a short circuit across the secondary -winding section |2, it4 is necessary to provide a current limiting resistor 3| which prevents this short circuit from causing any damage to the secondary winding.

Under normal conditions as soon as the ignition device 4 and burner motor 5 have been energized, there will be combustion which will be detected by the electronic iiame detector.

Brietly..the operation of the electronic name detector may be understood by the following description. The single electronic discharge device is shown with anode 66 and cathode 88 energized by a section of the transformer winding 54 connected through conductor |00, relay winding 51, conductor |00, anode 88, cathode 88, conductor ||0, and center tap 55 back to the secondary winding 54. Without any biasing voltage on the control element 81 the current flow through the electron discharge device 85 will be sufilcient to energize the relay 58. A biasing voltage for the electron discharge device 85 is provided by way of a connection to the left end of the secondary winding section 53, through conductor junction 2, conductor |3, resistor 13, conductor ||4, condenser 14, conductor ||5, conductor H8, and resistor 10, to the control element 81. With this connection to the control element 81, it can be seen that the alternating current present on the control element will be displaced in phase with the voltage present on the anode 68. With this phase displacement, the control element 81 will be negative when the anode 68 is positive. With this bias voltage, the' conductivity of the discharge device 85 will have been decreased sufficiently to cause the relay 56 to be deenergized and the switch'arms and contacts of the relay 58 will be in the position shown on the diagram,

The biasing network for the control element 61 actually consists of a circuit that may be traced from the center tap 55. through the con.- ductor ||0, conductor ||9, resistor 12, conductor IIB, condenser 1|, conductors ||1, ||8, and ||5, condenser 14,'conductor ||4, resistor 13, and conductors ||3 and back to the winding 53. From this it can be seen that the magnitude of the alternating current actually applied to the control element is less than that with the bias connection through resistor 13 and condenser 14 considered alone. However, it is still sutlicient in 'magnitude to maintain the discharge device eiectively non-conductive.

In order to put the relay 58 in an energized condition it is necessary to provide additional bias for the electron discharge device. This is accomplished when flame is sensed by the photocell 8. The photocell 8 is energized by the secondary winding section 53 through conductor junction I2, conductor |2|, terminal |22, conductor |23, photocell 8, conductor |24, terminal |25, conductor |28, resistor 15, conductors |21, |20, ||8. and ||1, condenser 1|, resistor 12, conductors I3 and I0 back to the center tap 55. As the photocell has unidirectional conductive properties on the presence of light, the application of alternating current to the photocell makes it act as a rectier in a manner to charge the condenser 1| plus 0n the control element side and minus on the .switch arm 68switch contact 58, conductor |33 Vconductor |32, switch contact I3, switch arm I8. .conductor |35, junction 88, and conductor 8Iiback .to the secondary winding. With this .last circuitv cathode side. With this charge on condenser 1I it can be seen that the control element now has bustion has been established. Upon the estab-- lishment of combustion, the photocell 8 will put a bias on the electron discharge device 85 which will in turn energize the relay 58. When relay 58 is energized, the switch arm 82 will move out of engagement with contact 83 and break the energizing circuit to the ignition device 4.

While the initial energizing circuit for relay winding I8 was completed through the switch arm 88 and switch contact 8| of the relay 58, the above traced holding circuit completed through the switch arm 2I and switch contact 28 of the relay I is independent of switch arm.88 and contact 8| so that the movement of the switch arm 88 from the contact 8| will have no eii'ect upon the energization of relay I5. 'Ihis starting circuit for relay I5 is necessary to provide for the situation that might arise when a momentary power failure occurs or when the thermostat contacts are accidentally opened. Were this starting arrangement not present. it would Vbe possible upon the recurrence of power, if the relay 58 should stick in the energized position, to have relay I5 become yenergized to start the burner 4 without any ignition present to ignite the fuel present. Therefore, since the ignition device 4"-is energized when relay 58 is deenergized it is advisable to have the starting circuit completed through contacts that are closed when the relay 58 is deenergized. l

With relay 58 energized the switch arm 58 now engages the switch contact 59 to complete a V`holding circuit for the relay |'5 independent ofthe safety switch device 25. The holding circuit vfor the relay I5 may now be traced through from the Asecondary winding section I3 through conductor 88,.relay winding I8, conductor 8|, terminal 82, switch ycontact 43, switch blade 42, terminal- 48, terminal |28, conductor |38. switch arm 2| Aswitch contact 28, conductor IBI, conductor 85,

remaining operative, the burner motor will helfenergized until such time as the heat from the burner motor has caused the thermostat 48 :move to the right and break the energizing circuit for the relay I5. Breaking of energizing circuit to relay l5 by the opening of the switch contacts of the thermostat allows the .switch arms I8, 2|

`and 23 to move out of engagement with their respective contacts I8, 28 and 22. When the switch arm 23 moves out of engagement with contact 22 the energizing circuit to the burner motor 5 -and ignition device 4 is opened and the system is shut down. As soon as the flame in the burner Adies out, the photocell 8 will not maintain the the thermostat 48 on a call for more heat.-

In :the event that the energizing of the igni-I tion device 4 and burner motor 5 does not iniratus will be shut down to prevent any damage. This is because the energizing circuit for the relay I5 is completed through the safety switch heater 28 and the contacts of switch arms 21 and 28. This circuit may be traced from the winding I3 through conductor 88, winding I8, conductor 8l, terminal 82, contact 43, switch blade 42, element 4I, terminal 48, terminal |28, conductor |38, switch arm 2|, contact 28, conductor I3I, terminal 88. switch arms 28 and 21, terminal 81, conductor 83, heater 28, conductor 88, Junction 98 and conductor 8| back to the winding I2. If this above traced circuit is allowed to remain energized for a predetermined length of time, it may be seen that the current ilow through the heater 28 will warp the bimetallic element 28 upward to allow the contacts of switch arms 21 and 23 to separate. The circuit to relay I5 will now be broken and the ignition device 4 and burner motor 5 will be deenergized thus preventing any further operation. The apparatus cannot be put back in operation until the reset member 38 is pressed to the right to allow the bimetal element to move back in a position to hold the contacts .of the arms 21 and 28 in a closed position. If

the contacts of the thermostat 48 are still in a closed position the relay I5 will be energized and the apparatus will again attempt to establish combustion.

Operation upon flame failure t Assume the system is operating normally with the burner motor functioning properly and relay 58 energized indicating a flame. y The safety switch device 25 in this condition will be shunted out In the manner just described. Should the fuel supply to the burner motor fail, combustion will cease, thus causing the flame detector photocell to cease supplying a rectified bias signal to the discharge device 55. The resulting decrease in conductivity of the discharge device 85 will ,cause deenergization of the relay 58 which in turn will move the switch arms 88 and 82 to the deenergized position. Deenergization of relay 58 causes the switch arm 82 to engage the contact 53 and put the ignition device back in Voperation nin `an attempt to initiate combustion again. The

switch device so that the safety switch heater` 28 is now operative in the circuit traced above vthrough the heater 28 to the relay winding I8.

After a certain time delay the heating action of Athe safety switch heater 28 will warp the bimetal element 23 in an upward direction. If combustion is not reestablished in the meantime, as soon as the bimetal 28 has warped sufficiently the circuit for the relay I5 will be opened as described above when no name occurred when the burner was put in operation. The opening of the circuit will cause the deenergization of the relay I5 which in turn will deenergize the entire system. If combustion is reestablished, relay 58 will again be energized to shunt out the safety switch heater again as described in connection with a normal starting cycle. I

1 Operation upon a false indication of flame If, for any reason, the relay is maintained in an energized position when the thermostat 48 has -been satised the system will be rendered inoperative by the action of the safety switch. This may readily be seen when a circuit is traced from the -tap I4 of the secondary winding of transformer combustion, it may be seen that the appa- 'a I8 through the resistor 3|, conductor |34, conductor |33, switch contact 59, switch arm 60, conductor 85, terminal 66, switch contacts 21 and 28, terminal 81, conductor 88, energizing' element 26, conductor 89, junction 80, and conductor 8| back to the secondary winding. With the safety switch heater 26 of the safety switch 25 energized in this manner, the resultant opening of the contacts 21 and 28 will make it impossible to have an energizing circuit for the re-ay l should the thermostat 40 call for more heat. Manual intervention is required to put the apparatus back in operation again. This is done by pressing the reset member 30 to the right to close the contacts of the switch arms 21 4and 28 as described above.

Figure 2 In the modification shown in Figure 2, ran apparatus has been provided which will distinguish between a flame failure and a false indication of flame. It differs from the apparatus shown in Figure 1 in that upon a false indication of flame the safety switch heater is maintained energized continuously and manual intervention cannot put the apparatus back in operation until the trouble has been cleared from the apparatus.

The flame detection circuit and the burner apparatus are the same as shown in Figure 1. All elements common to the two figures carry the same reference numerals. A transformer |50 has a primary winding |5| connected to the power lines l and 2. Two secondary windings, |52 and |53 form energizing circuits for a relay |54 and a safety switch |62 in a manner to be described hereinafter. The relay |54 consists of a winding |55, armature |56, switch arms |58 and |59, and switch contacts |51, |60, and |6|. The safety switch device |62, includes a safety switch heater |63 and a bimetallic element |64 which is adapted to move in an upward direction when heated sufficiently by the heating cement |63. The safety switch also includes switch contacts |65 and |66 which are normally engaged in the position shown until such time as the element |64 has warped sufficiently upward to allow the arm carrying the switch contact |65, which is biased toward the left, to break the connection between the contacts |65 and |66. The safety switch |62 also comprises another pair of contacts |61 and |68 which will be closed when the arm carrying the switch contact |68 has been allowed to move toward the left to break the contacts |65 and |66.

A reset member |69 has been provided to put the system back into the position shown once the bimetal has been moved into the safety position. Located in thermostat housing |10 is a thermostat having a blade |1| positioned by a bimetallic element and having an associated contact |12. Also conveniently located with the thermostat may be an alarm |13.

Operation of Figure 2 When the heating condition has been satisfied the elements are in the position shown on the dagram. Upon a call for heat in an enclosure where the thermostat housing |10 is located the blade |1| of the thermostat will move towards the left into engagement with the contact |12. The closing of this contact will complete an en ergizing circuit for the relay |54 which may be traced from the secondary winding |52 through the conductor |9I, terminal |90, contact |12, blade |1|, conductor 203, terminal |89, conductor |88, terminal |81, switch contacts |65 and 66, terminal |86, conductor |85, heating element |63, conductor |84, secondary winding |53, conductor 85, switch arm 60. contact 6|, conductor |83, relay winding |55, conductor |82, junction winding |52. Energizing of relay |54 causes the switch arm |59 to move into engagement with contact |60 to form a completecircuit lor the ignition device 4 which may be traced from the power line through conductor |92, contact |60, switch arm |59, conductor |93, junction 95, switch contact 63, switch arm 52, conductor 96, terminal 91, conductor 88, through the ignition device 4 to conductor 89, terminal |00, and junction |0| of the power line 2. As in Figure l, the energizing circuit for the burner motor 5 may be traced from the junction that is common with the ignition circuit through the conductor |02, terminal |03, conductor |04, through the burner motor to conductor |05, terminal |06, and junction |01 of line 2. Energizing of relay |54 also moves switch arm |58 into engagement with contact |5| to provide a holding circuit for relay |54 that is independent of the switch arm 60 and contact 6| of the relay 56. This circuit may be traced from the secondary winding |52 through the conductor |9I', terminal |80, switch contact |12, blade |1|, conductor 203, terminal |89, conductor |88, terminal |81, switch contacts |65 and |66, terminal |86, conductor |84, switch arm |58, contact |51, winding |55, conductor |82, junction |8|, and conductor |80 back to the secondary winding |52. The secondary winding |53 is still energizing the safety switch heater |63 by way of conductor 85, switch arm 60, switch contact 6|, conductor |83, contact |51, switch arm |58, conductor |94, terminal |86, conductor |85, safety switch heater |63, and conductor |84.

As soon as flame has been established by the burner motor and the ignition device the relay 56 will be energized in a manner previously described in connection with Figure 1. Energizing of relay 56 will move the switch arm 62 out of engagement of contact 63 to thereby deenergize the ignition device 4. The energizing of relay 56 also moves the switch arm 60 out of engagement with contact 6| to thereby open the circuit to the safety switch heater to thereby prevent the safety switch heater from shutting down the system. Thereafter, as with the previous arrangement, the system will continue to operate until the thermostat becomes satisfied or untilthere is a combustion failure.

Operation upon a flame failure Assume again the system is in normal operation with the burner motor functioning properly and the relay 56 energized indicating afiame. As previously explained the safety switch device |62 is not energized since the safety switch heater |63 does not have any energizing circuit. Should a flame failure occur, due to lack of fuel or faulty operation of the burner motor the relay 56 will be deenergized. When this occurs, the circuit to the ignition device 4 has been reestablished. A completed circuit is also established for the safety switch heater |63 from winding |53 through conductor 85, switch arm 60, switch contact 6| conductor |03, switch contact |51, switch arm |58, conductor |94, terminal |86, conductor |85, heater |63, and conductor |84. If a flame is not detected after a predetermined time, the bimetallic element |64 will have warped sufciently to allow the switch contacts |65 and |56 to separate to thereby break the energizing circuit to the relay |54. The movement of the arm carrying the switch contact |85 toward the left causes the contact |68 to engage the contact |61 and form a circuit for the alarm which may be traced from the secondary winding |52 through the conductor |9I, terminal |99, contact |12, vblade |1I, conductor 283, terminal |89, conductor |88, terminal |81, switch contacts |168, and |81, terminal |95, conductor 202,l terminal |96, conductor |91, the alarm |18, conductor |88, terminal |99, conductor 288, junction |8|, and conductor |89 back to the secondary winding |52. Although this particular diagram shows the alarm circuit completed through the thermostat, it is to be understood that any suitable alarm circuit could be completed by way of contacts |61 and |68.

With relay |54 deenergized and relay 58 deenergized, it is not possible to complete an energizing circuit for the safety switch heater element |89. When it is desired to restart after such a shutdown, the reset member |69 is depressed to allow the element |64 to go back into the position shown on the diagram. The switch contacts |85-and 66 will then be in a position. to allow energization of relay |54. It is therefore possible for the system to start operation again'in the manner just described and should the flame -appended claims.

substituted. Too, it will be obvious to those skilled in the art that various modifications will suggest themselves and therefore I intend my invention to be limited only by the scope of the I claim as my invention:

l. In combination, a power source having a transformer secondary winding, first and second relay means each having a plurality of switch arms and contacts, a current limiting impedance connected to a ,point on said power source and one of the contacts of each of said rst and second relay means, a safety switch having energizing means and switch contacts in a series connection, saidcontacts being opened by said means after a period of energization, means connecting A one end of said safety switch to said power source not be detected the system will go out on the l safety switch shut down as just described.

Operation upon a false indication of flame Should the relay 56 remain energized when the relay 154 is deenergized due to some type of failure in the ame detecting apparatus when there actually is no flame present in the burner, a circuit is established for the safety switch heater |63. This circuit may be traced by way of conductor 85, switch arm 68, contact 59, conductor 28|, contact |6|, switch arm |58, conductor |94, terminal |86, conductor |85, safety switch heater |63, and conductor |84 back to the secondary winding |58'. After a predetermined time delay,

and a. switch arm of said first relay means, means connecting the other end of said safety switch to a further contact and a switch arm of said first and second relay means respectively, a first condition responsive device connected to completean energizing circuit for said first relay means through said safety switch and a switch arm and contact of said second relay means, a second conditionresponsive device adapted to energize said second relay means and deenergize said safety switch to prevent the deenergization of said first relay means, and means including said current limiting device, said power source, and certain of the switch arms and contacts of said second relay means for energizing said safetyswitch independently of said rst condi tionresponsive device when said rst relay means is deenergized and said second relay means is energized to' thereby maintain said first relay y means inoperative. i

2. In a control apparatus for a fuel burner, a

gize a fuel burner, a combustion responsive de- Mergized by the transformer winding |53 and will "fnot allow the bimetal to return to the position ,ratus in which the safety switch has been uti- .'lized to provide a shut down upon. a flame failure :or upon the false indication of iiame. Too by la slight modification, I haveprovided a control vapparatus' which .utilizes the safety switch to 'shut the apparatus down in case of a failure and l,to distinguish between a iiame failure and a 'false the above, I have ensured that the apparatus "indication of flame. 'Too, in cooperation with of my invention will start in the proper sequence.

I have shown my invention in connection with an electronic flame detector and while it is applied well there it is to be understood that any of combustion responsive device could be vice adapted to indicate proper operation of the burner, a safety switch operable to deenergize said first named means upon failure of operation of said combustion responsive device, said safety switch comprising a pair of contacts and an actuator therefor` which is effective after a, period of energization to open said contacts, means con-` necting said combustion responsive device to said safety switch to render said safety switch inoperative and maintain said rst named means operative independently of said safety switch upon proper operation of said combustion responsive, device, and further means connecting said combustion responsive device in an actuating circuit independently of said temperature responsive device with said safety switch to render said safety switch operative when said combustion, responsive device is falsely indicating combustion to maintain said first named means inoperative. 3. In a control apparatus for a fuel burner, a temperature responsive device, means actuated by said temperature responsive device to energize the fuel burner, a combustion responsive device adapted to indicate proper operation of the burner, a reset safety switch having a pair of switch contacts and an actuator therefor operable after a period of energization of said actuator to cause said switch to deenergize said rst named means upon failure of operation of said combustion responsivel device, means connecting said combustion responsive device to said safety I switch to disconnect said safety switch actuator and maintain-said rst named means operative 4upon proper operation of the burner, and furenergizing said first relay means including said power source and said controlling means, second relay means adapted when energized to indicate operation of the heating apparatus, means including said power source for energizing said last named relay means upon operation of the heating apparatus, a safety switch device having an actuator therefor operable when energized for a predet;rmined time to cause said safety switch to render said rst relay means inoperative, means including said power source for energizing said safety switch device through said first relay means when said first relay means is energized, means including contacts of said second relay means when energized for maintaining said first relay means operative independently of said actuator of said safety switch, and means including said source of power for energizing said safety switch device independently of said first relay means and said controlling means when said second relaymeans is falsely indicatlng operation of the heating apparatus and said first relay means is deenergized.

5. In a control apparatus for heating appara-` tus, a power source, first relay means adapted when energized to initiate operation of the heat- 'ing apparatus, switch means indicative of the need for operation of the heating apparatus, means including said switch means and said source of .power for energizing said first relay means, an electrically operable out off device having an actuator which is operative after a predetermined time d;lay to cause said device tobe effective, means connecting said cut off device in a series connection with said first relay means, second relay means adapted to be energlzed by said source of power upon operation of the heating apparatus, means connecting said second relay means in circuit with said cut off device to render said cut off device inoperative when both of said relay means are operative, and means connecting said cut off device in circuit with said second relay means independently of said switch means and said first relay means when said second relay means falsely indicates operation of the heating apparatus.

6. In a control apparatus for heating apparatus; a power source comprising a transformer having a tappzd secondary winding; first and second relay means each having a plurality of switch contacts said first relay means adapted to initiate operation of the heating apparatus, and said second relay means adapted to indicate proper operation of the heating apparatus; a safety switch, said safety switch comprising a pair of contacts and an actuator therefor which when energized for a predetermined period of time will open said contacts; a condition responsive device;'a series circuit comprising said first relay means, said power source, said safety switch, contacts of said second relay means, and said condition responsive device, said series circuit when completed by the actuation ofl said condition responsive device causing energization of said first relay means; means'adapted to energize the heating apparatus upon energlzation of said first relay means; means including said second relay means when energized by proper operation of the heating apparatus for maintaining said first relay energized independently of the energizing means of said safety switch; and means connecting a portion of said power sour'ce in circuit with certain switch contacts of said second relay means in such a manner that when said second relay means is energized and said first relay means is deenergized the energizing means of said safety switch will actuate said safety switch to maintain said series circuit inop` erable when said condition responsive device closes to thereby maintain the heating apparatus inoperative.

7. In a control apparatus for a fuel burner; a power source; a control device; means; means for energizing the fuel burner including said power source, said control device and said first relay means; a combustion responsive device adapted to indicate proper operation of the burner; second relay means energized by said combustion responsive device; a timedv safety switch having energizing means and switch concontacts connected in a circuiti/ith said first relay means; a plurality of switch arms and contacts associatedwith said first and second relay means adaptd to render said safety switch inoperative when both of said relay means are operative; and means interconnecting certain of said switch arms and contacts so that said safety switch will be energized independently of said first relay means and said control device by said power source when said second relay means-is energized falsely by said combustion responsive device and said first relay is deenergized to thereby prevent operation of said rst relay means and the fuel burner.

8. In a control apparatus for a fuel burner, a control device having switch contacts, a source of power, a first relay having a plurality of contacts adapted when actuated to initiate operation of the burner, means including the contacts of said control device for connecting said first relay in an energizing circuit to said source-of power, a safety switch having a heater therefor, means connecting the heater of said safety switch in the energizing circuit of said first relay when said first relay is initially energized by said control device, a second relay, means for energizing said second relay upon proper operation of the burner, means includingr said second relay for maintaining said first relay in an energized circuit independently of the hxater of said safety switch, and means connecting the heater of said safety switch in an energizing circuit independently of any actuated switch contacts of either of said control device or said first relay means when said second relay is falsely indicating proper operation of the burn;r.

9. A control apparatus for a fuel burner system having a control switch for indicating the need for burner operation, the combination comprisng, a source of power, a rst relay adapted to actuate the fuel burner when energized, a safety switch having a heater therefor, an energizing circuit for connecting said first relay to Said source of power adapted to be completed by means including the control switch and the heater of said safety switch, a second relay adapted to be energized by means indicative of proper operation of the burner, means including said second relay when energized for maintainfirst relay` i 1s ing said first relay energized independently of the heater of saidsafety switch, and'means for connecting the heater of said safety switch in an energizing circuit when said first relay is de- ,energizedand said second relay as falsely indicating operation of the -burner.y f

10. A control apparatus for a fuel burner system having a temperature responsive switch for indicating the -need for burner operation. the combination comprising, a' source of power, a first relay having an energizing winding therefore and adapted when'energized to initiate operation ofthe burner, asafety switch having switch contacts and an -actuating heater therefor, energizing circuit means 'adapted to include te'mperature'responsive switch and the heatgal Vrelay means for deenergizing the heaterof said safety switch when the burner is operating properly, and means for connecting the heater of said i safety switch in an energizing circuit that is independent of said temperature responsive switch and the energizing winding of vsaid first relay to said source of power when said first relay is de. .energized and said second relay is falsely indieating proper operation -of the burner.

1l. A control apparatus for a fuel burner system having a control switch for indicating' the need for burner operation, the combination comprising, a source of power, rst relay means adapted to be energized by said source upon the closing of the 'control switch for renderingroperative the fuel burner, a safety switch i'or effecting burner shutdown connected in series with said first relay means, said safety switch having an actuator which is operative to cause said safety switch to deenergize said first relay means after said actuator has been energized a predetermined time, second rrlay means adapted to be energized by means including said power source upon the proper functioning of the fuel burner and operative to deenergize said safety switch and maintain said first relay means in an energized circuit independently of said safety switch, and means interconnecting said second,

relay means and said power source such that, following a pred termined time interval, deenergization of said rst relaymeans when said second relay means is energized will cause said power source to energize the actuator of said safety switch independently of said control switch to maintain said first relay means inoperative thereby preventing further operation of the fuel burner.

12. A control apparatus for a fuel burner system having a control switch for indicating the need for burner operation, the combination comprising, a source of power, first relay means `lli said safety switch, and rendering said safety switch inoperative, and means connecting said .controldevice in a circuit with the actuator of said safety switch independently ofthe control switch such that if said control device indicates combustion when said first relay eans is deenergized, said safety switch will maintain said first relay mi ans inoperative upon the closing of the control switch to prevent further operation of the fuel burner. i

13. In a control apparatus for a fuel burner, a power source, a control switch, first relay means having a ,plurality of switch arms and contacts,

means for energizing said first relay means inv relay means, a safety switch having a pair of adapted to be energzed by said source upon the A closing of the control switch and to render operative the burner, a safety switch for effecting burner shutdown connected in series with said first relay means, said safety switch having an actuator which is operative to cause said safety switch to deenergize said first relay means after said actuator has been energized a predetermined time, a control device adapted to be rendered operative by means indicating proper operation of the burner, circuit means including said control device maintaining saidiirst relay contacts and a single actuator therefor, and

.electrical means connecting saidv contacts in controlling relation to said first relay means and said actuator in'- an electrical circuit so that said actuator will cause said safety switch to render said first relay means inoperative when said one of said last named circuits is completed through said actuator upon continued energization of said second relay means when the burner is inoperative or to render said first relay means inoperative when another of said last named circuits is completd through said actuator upon energization of the burner with said second relay means remaining inoperative.

14. In a control apparatus for a fuel burner, a source of power, rst means adapted to respond to a condition indicative of the need for burner operation to energize the burner, further means adapted to respond to a condition indicative of prop'r operation of the burner, and means adapted to render said first named means inoperative either upon a failure of said further means to indicateproper operation of the burner or upon continued operation of said further means with said first namedv means inoperative, said last named means comprising a safety cutoff device having an actuator therefor which is effective when energiz'd for a predetermined time to actuate said safety switch, a plurality of electrical circuits controlled by said condition responsive means and said further means, means including said power source and one of said circuits for energizing said actuator of said cutoff device independently of said first named m-'ans when said further means is operative and the burner is inoperative, and means including a further of said circuits for maintaining the fuel burner operative independently of said actuator if both said condition responsive means and said further means are operative.

15. In an electronic control apparatus for a fuel burner, a power source, a temperature responsive device, energizing means for establishing combustion in the fuel burner, operable means for actuating said energizing means upon the operation of said temperature responsive device, relay means, an electron discharge device having operable circuits therefor to energize "means in an energized circuit independently of said relay lmeans upon a condition of proper operation of the fuel burner, a time delay safety switch means having an actuator connected in circuit with said operable means to render said operable means inoperative when said electron discharge device fails to operate said relay means, means including said relay means shunting said safety switch means actuator from the circuit of said operable means upon proper operation of the burner, land further means independent of said temperature responsivesdevice interconnecting said relay means and 4said operable means to actuate said safety switch means actuator when said electron discharge device is operating and said operable means is deenergized to thereby maintain said operable means inoperative upon a further operation of said temperature responsive device.

16. In a control apparatus for a fuel burner, a power source, an electron discharge device having an anode, cathode and control elements. a temperature responsive device, a ilrst relay adapted to energize the fuel burner upon the actuation of said temperature responsive device, a combustion responsive device for indicating proper operation of the burner, a second relay connected in circuit with the anode of said electron 'discharge device, means connecting said combustion responsive device to said electron discharge deviceso that upon the occurrence of combustion at the burner said second relay means will be energized, a safety switch having a pair of contacts and an actuator therefor which will open said contacts after a predetermined time delay, means connecting said safety switch in a series circuit with said rst relay means independently of said second relay when thelatter is energized, circuit means including said second relay for energizing said first relay means independently of said safety switch actuator, and further means for energizing said safety switch actuator by said power source independently of said temperature responsive device when said first relay means is deenergized and said second relay means is energized due to faulty operation of said combustion responsive device to thereby prevent operation of said first relay means and the burner upon a further operation of said temperature responsive device.

17. A control apparatus for a fuel burner, a power source, first electrical means adapted to respond to a condition indicative of the need for burner operation operable to energize the burner, further electrical means adapted to respond to a condition indicative of proper operation of the burner, said further means comprising a thermionic electron discharge device having a fllamentary heater which is normally continuously enzrgized, said heater having a time delay upon energization thereof, following an appreciable period of deenergization, before thermionic emission occurs which delay is greater than the time required for energization of said first electrical means, and means adapted to render said first named means inoperative either upon a failure of said further means to respond toa condition indicating proper operation of the burner or upon continued operation :ssl

of said further means when means is inoperative.

18. Control apparatus for a fuel burner, comprising'a source of power, first switching means adapted when actuated to a ilrst position to initiate burner operation, second switching means for indicating proper burner operation when actuated to a first position and lack of burner operation when actuated to a second position. said second switching means being controlled by a' thermionic discharge device havingv a filamentary heater therefor which has an appreciable time delay in heating to a degree where said device will be in a condition to conduct. means normally continuously connecting said heater to said source, a timed safety switch having a heater therefor and switch contacts connected to render the burner inoperative when said contacts are open, and means connecting said source to said last named heater when operation of the burner is not safe, said last named means comprising said first switching means when in said first position with said second switching means in said second position or. said second switching means when in said first position with said first switching means not in said first position.

19. A control apparatus for a fuel burner system having a control switch for indicating the need for burner operation, the combination comprising, a source 'of power, first relay means adapted to be energized by said source upon the closing of the control switch for rendering operative the fuel burner, a safety switch for effecting burner shutdown, said safety switch having an actuator connected in series with said first relay means and operative to cause burner shutdown after said actuator has been energized a predetermined time, second relay means adapted to be energized by means including said power source upon the proper functioning of the fuel burner and operative to effectively deenergize said safety switch actuator and maintain said first relay means in an energized circuit independently of said safety switch actuator, and means interconnecting said second relay means and said power source such that, following a predetermined time interval, deenergization of said first relay means when said second relay means is energized will cause said power source to energize said actuator independently of said control switch to maintain said apparatus inoperative thereby preventing further operation of the fuel burner. i

JOHN M. WILSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name y Date 2,075,289 Judson Mar. 30, 1937 2,102,618 Francis Dec. 21, 1937 2,102,691 Francis Dec. 2l, 1937 2,254,984 Tate Sept. 2, 1941 2,274,384 Scanlan Feb. 24, 1942 said first named 

